The invention relates to fuel injectors having injection nozzles controlled by a nozzle needle or the like, and having a control chamber, which communicates with a high- and a low-pressure side of the injector, which is designed as a working chamber of a displacer coupled to the nozzle needle for driving, and which is switched by means of a control valve arrangement between a closing pressure, at which the nozzle needle is set to the closed position thereof by the displacer, and an opening pressure, at which the nozzle needle, together with the displacer, moves into the open position.
In the case of a fuel injector known from DE 10 2007 060 395 A1, the nozzle needle has an end remote from the nozzle which is designed in the manner of a plunger and is arranged so as to act as a displacer in the control chamber. This control chamber communicates by way of an inlet restrictor with the high-pressure side of the fuel injector and can be connected by means of the control valve arrangement to the low-pressure side of the fuel injector. When the control valve arrangement is closed, the control chamber is connected only to the high-pressure side of the injector, whereas, when the control valve arrangement is open, the pressure in the control chamber falls owing to the additional connection which is then present between the control chamber and the low-pressure side. In this known fuel injector, the control chamber has an outlet duct which opens to the low-pressure side of a valve body and which is controlled by a sleeve-shaped closing body of the control valve arrangement. This sleeve-shaped closing body is arranged movably on a guide rod coaxial with the outlet duct, wherein the annular gap between the outer circumference of the guide rod and the inner circumference of the sleeve-shaped closing body is designed as a virtually leakage-free sealing gap. The sleeve-shaped closing body interacts with a seat concentric with the mouth of the outlet duct and is connected to an armature which, for its part, interacts with an electromagnet arrangement coaxial with the guide rod. If the electromagnet arrangement is electrically energized, the armature, together with the sleeve-shaped closing body, is pulled in the direction of the electromagnet arrangement, with the result that the closing body rises from its seat. In the electrically unenergized condition of the electromagnet arrangement, the closing body is set to the closing position thereof by a closing spring and the armature moves away from the electromagnet arrangement.
Fundamentally, the aim is to be able to determine accurately the operating phases of a fuel injector in order to allow optimum engine control. Wear phenomena on the fuel injector cause drift in the closing times of the nozzle needle, with the result that there is a corresponding change in the quantities of fuel injected and the engine concerned no longer operates in an optimum manner if adaptation of the fuel injector and the engine to the changed operating circumstances is not possible. Moreover, the injectors also exhibit series tolerances in the quantity injected, owing to unavoidable variation in components, even if each injector is activated in the same way.